The present invention is a vertical gang saw for cutting hard materials. It comprises a body supporting the vertical frame, which is equipped with a series of gang saw blades held vertically that are activated in a backward-forward, up-and-down motion. There is also a support table holding the material to be sawed.
In particular, this invention concerns a machine with reciprocating vertical movement of the blades in which the sawing takes place in two directions.
From patent document FR-A-2498977, a saw with multiple gang saw blades to cut large blocks of marble or stone into slabs is already known. A vertical frame having relatively short saw blades is engaged with an up-and-down movement. This permits the sawing of blocks of practically unlimited length during the two displacment movements of the saw frame. The frame is guided at the midpoint and at the upper extremity of each of its sides by two Watt guide systems, each having a lever connected at each of its ends to a beam oscillating around a fixed pivot. This setup permits an approximately rectilinear guide for the frame.
In this guidance system, one of the beams can be activated by an eccentric gear in order to ensure a saw curve that is essentially circular, in order to reduce the number of teeth engaged with the block.
The eccentric gear is driven at the same rotation speed as the flywheel driving the reciprocating movement of the vertical frame. The Watt guide rods oscillate, therefore, in phase with the vertical frame.
A sophisticated balancing system compensates for the inertial forces of the parts undergoing a reciprocating movement. The system permits a speed of 260 cuts per minute.
The main disadvantage of this improved Watt arrangement lies in a fault in the sawing curve in the sense that the locus of the successive positions of the blades is an irregular curve that creates high pressure points on each of the blades at certain moments during the rocking of the frame.
These pressure points subject the levers and beams of the guidance system, and, especially, the pivot pins, to enormous stresses, which brings about premature wear of these pivot pins.
Belgian Patent No. 529856 shows a gang saw composed of one or several armored blades fixed to a vertical frame driven in a reciprocating, up-and-down, vertical movement by a crankshaft activated by a flywheel. A support table brings the marble or stone block into engagement with the saw teeth in an essentially perpendicular orientation and permits the saw plane to cross the fixed plane of the block being sawed.
The vertical orientation of the frame permits the machine to saw blocks of indefinite length, with relatively short blades, in a manner that avoids all undesirable deviations of the blade.
The machine in the Belgian patent uses gang saw blades with hard-metal teeth that are suitable for cutting during displacement in only one direction.
In order to permit a gradual cut of a block during the downward movement of the frame and to permit the disengagement of the blades during the upward movement of the frame, a synchronized swing (pendular) movement is imparted to the four corners of the frame by four connecting rods, which are interlocked by forks having four horizontal guide rods. The connecting rods are driven by four cams maintained in synchronous rotation by the main shaft that drives the saw frame.
The combination of the vertical reciprocating movement of the saw and the horizontal swing movement creates a more or less flat, ovoidal sawing trajectory, permitting a gradual penetration of the teeth along a gentle curve in one direction and the disengagement of the teeth from the marble or stone in the other direction.
Also, because of the ovoidal curve, all the blade teeth are not used with the same severity.
In each cycle, the raising of the saw blade to disengage the teeth regularly shields the blade from the pressure of sawing and permits a repeated but total abatement of this pressure. The subsequent engagement of the teeth to the stone, up to a predetermined contact pressure, induces high stresses in the blade and provokes cyclic blade deformations that are not negligible; thus the blade experiences considerable fatigue stresses and strains. These cyclical deformations of the blade lead to displacement of the blade and unfavorably influence the cleanness of the cut in the marble or stone.